Symbols vs OpeningBook

Learn logic with Symbols, the app that teaches natural deduction and the rules of inference in an intuitive, accessible way. Our unique Studycards feature visual pictographs and interactive, step-by-step exercises that allow you to grasp each rule easily and quickly. Then, challenge yourself with activities specifically designed to practice those rules, building your skills progressively, and cementing them in your memory with every level completed. Why Symbols? Comprehensive Studycards: Learn essential rules like Modus Ponens, Modus Tollens, Disjunctive Syllogism, and many more through clear explanations and examples. Perfect for students and anyone looking to understand formal logic. Engaging Activities for Skill Mastery: Validity: Sharpen your critical thinking by evaluating pre-solved arguments. This unique activity provides the benefits of repetition without the tedium, helping you apply, recognize, and grow familiar with the rules of inference. Justification: Challenge your understanding with puzzle-like scenarios where you deduce missing argument steps. This deepens your comprehension and refines your application of logical rules within complex arguments. Inference: By this stage, the training wheels are off, and the student has to draw on everything they've learned so far. Their task is to mentally build a valid argument from what’s provided—or to recognize that no valid argument can be formed. What would normally be worked out slowly on paper is now done at the speed of thought. Translation: Translation helps students practice turning statements with indicator words and phrases into logical form. These indicator words, commonly found in logic books and courses, give students a sense of how to translate everyday language into formal logic. Translation breaks this process into levels, allowing students to track their progress and earn new scores as they build proficiency. Download Symbols for free and begin your journey into formal logic. Your free access includes the first level of every activity and the Modus Ponens study card, a must-have for getting started. For more advanced content and features, simply use our in-app purchases to continue building your logic skills. Start your journey of mastering the rules of inference now!

OpeningBook is a clean, offline reference and trainer for chess openings. BROWSE EVERYTHING • Thousands of named openings and variations, organized by ECO volume (A–E), family, and line — sourced from the open Lichess openings database. • Step through any line move-by-move on a real, playable board. • Read key ideas and classic traps for the major openings. SEARCH & FILTER • Find any opening by name, ECO code, or move sequence. • Filter by line length with a simple move-count slider. TRAIN YOUR REPERTOIRE • Add lines to your training set as White or Black. • Drill them in a play-your-side-vs-app loop. • Spaced repetition brings each line back for review at the right time. 100% offline. No account, no ads, no tracking.