|Inserting: in a formula an icon can be replaced under certain conditions by another icon. E.g. inserting a constant for a variable will make a propositional function become a sentence. See also substitutability, substitution, validity, statements, propositional functions.|
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|Substitution (Insertion)||I 202f
Rule of substitution/insertion/QL: 1. In A i is replaced only at the places where it occurs freely - 2. If i in A is in an area where a quantifier binds the variable h, no expression may be used for i which contains h as free variable - ((s) E.g. ("h)(P(h)ui): here i should not mean "h u y") - "everything I own are bicycles and also a bike ... " - E.g. Wessel: Solo guide: from A follows AiA:A: "x is born later than 1930"> "x is less than 100 years old" - if i would occur free in the assumptions of the proof then wrong: "all people are born later than in 1930".
Logik Berlin 1999