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 Dec29 answered Skolemization of a Formula Dec29 comment Why is 'abuse of notation' tolerated? Without further research you are saying that I were using non-standard notation. May I show you the following reference: ISO 31-11: ⇒ p ⇒ q implication sign if p then q; p implies q Can also be written as q ⇐ p. Sometimes → is used. en.wikipedia.org/wiki/ISO_31-11 . Seems you are suffering from some severe self overestimates, the only thing that is distracting here. Dec29 revised Skolemization of a Formula edited tags Dec29 revised Skolemization of a Formula deleted 99 characters in body Dec29 revised Skolemization of a Formula added 98 characters in body Dec29 asked Skolemization of a Formula Dec29 revised Is the validity of the Skolemization of a sentence A infers the validity of A? edited body Dec29 answered Is the validity of the Skolemization of a sentence A infers the validity of A? Sep25 comment What are the historical roots of cryptarithmetic? This is a hukumenzan: janko.at/Raetsel/Nikoli/Hukumenzan.htm . Somebody told me the translation is "prune and peach are friends", and the script is Hiragana. Sep23 comment What are the historical roots of cryptarithmetic? Looks they are called nowadays hukumenzan in Japan. But how about China? I still don't know. Sep23 comment Induction, how often? I have constructed the example from the property that ∀x doesn't preserve countable infinite ascending unions. The existential quantifier does so. But I am not yet sure what the implications are for induction. Maybe one can construct a predicate q, prove it by a single induction, and then derive p. Like following the odd numbers and hypothetically following the even numbers at the same time, and joining the two together resolving the hypothesis. The hypothesis would be p(1). Sep23 revised Induction, how often? added 43 characters in body Sep23 comment Induction, how often? Greetings from CH to CH. Looks like an agreement that ∀x p(x) holds. But somehow the proof doesn't go through with a single induction over p, does it? Sep23 revised Induction, how often? deleted 1 characters in body Sep23 asked Induction, how often? Sep22 comment Why does the expression of Peano induction has to be second order? Actually first order induction means that one adds a schema. So the X is really quantified, but not in the object logic but syntactically on the meta-level. Sep21 revised What are the historical roots of cryptarithmetic? added 58 characters in body Sep21 answered How to prove AB is not equal to BC Sep21 asked What are the historical roots of cryptarithmetic? Aug25 revised What kind of logics satisfy the coincidence lemma? added 286 characters in body; edited title