--- title: Olympiad: logic traps and if-then ★★★ — a lesson of Mova's school · trees and pragmatics description: «Olympiad: logic traps and if-then ★★★», a lesson of the world course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: Logic puzzles are built from small, safe moves: if A always brings B and there is no B, then there was no A. --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [World](https://md.mova.elamur.ai/free/en/corpora/school/world/) / Olympiad: logic traps and if-then ★★★ # Olympiad: logic traps and if-then ★★★ Lesson 193 of the world course of Mova's primary school: 20 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/world/193-olympiad-logic-traps-and-if-then/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/0/) — Logic puzzles are built from small, safe moves: if A always brings B and there is no B, then there was no A. - [2](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/2/) — To test a rule, look only where it could break. - [3](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/3/) — "If a card has a vowel on one side, it has an even number on the other": a card showing A could break it, and so could a card showing 7, but a card showing 4 can't, whatever is on its back. - [4](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/4/) — Picture an island where some people always tell the truth and some always lie. - [5](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/5/) — Nobody there can ever say "I am a liar": a truth-teller would be lying and a liar would be telling the truth. - [6](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/6/) — Order puzzles need care too: "Ann is taller than Ben, and Cal is taller than Ben" tells you who is shortest, but not who is tallest. - [7](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/7/) — Words like "all", "some", "not all" and "only" carry the whole puzzle. - [8](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/8/) — The opposite of "all the kids came" is not "no kids came" but "at least one kid didn't come". - [10](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/10/) — To check "if a card has a vowel on one side, it has an even number on the other" with cards showing A, K, 4 and 7, you must turn over A and 7, and no others. - [11](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/11/) — On an island of truth-tellers and liars, nobody can say "I am a liar"; if two people there say "the other one is a liar" and "we both tell the truth", the first is a truth-teller and the second a liar. - [12](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/12/) — "Ann is taller than Ben and Cal is taller than Ben" shows Ben is the shortest but doesn't say whether Ann or Cal is taller. - [13](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/13/) — The opposite of "all the kids came" is "at least one kid didn't come". - [14](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/14/) — "Some cats are black and some black things are bats" does not mean some cats are bats; the black cats and the black bats can be different animals. - [15](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/15/) — "Only people with tickets get in" means anyone who got in had a ticket; it doesn't promise that everyone with a ticket got in. - [16](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/16/) — One true example against an "all" claim, like a penguin against "all birds can fly", is enough to show it is false. - [17](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/17/) — A fair coin has a half chance of heads on every throw, even after 5 heads in a row; it has no memory. - [18](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/18/) — "It's not untrue" means "it's true": two "nots" cancel. - [19](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/19/) — When three boxes are labelled Apples, Oranges and Mixed and every label is wrong, taking one fruit from the box labelled Mixed is enough to put all three labels right. - [20](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/20/) — Ice cream sales and sunburn go up together because hot sunny days cause both, not because ice cream causes sunburn. - [21](https://md.mova.elamur.ai/free/en/corpora/school/world/193-olympiad-logic-traps-and-if-then/21/) — Words people use: "sus" means suspicious; "mid" means just average, not good; "ken" (Scotland) means know; "gadgie" (North East England) means a man, a bloke; "yinz" (Pittsburgh, USA) means you all. - ← previous: [Olympiad: time and calendar puzzles ★★★](https://md.mova.elamur.ai/free/en/corpora/school/world/192-olympiad-time-and-calendar-puzzles/) - next →: [Olympiad: everyday reasoning ★★★](https://md.mova.elamur.ai/free/en/corpora/school/world/194-olympiad-everyday-reasoning/) - ↑ back to [World](https://md.mova.elamur.ai/free/en/corpora/school/world/)