Add length of a propositional formula function in the Logic Module

[Medha210699]

This function returns the length of a formula (parentheses and spaces are ignored).
Useful for proofs by induction on the length of a propositional formula.

sage: f = propcalc.formula("a")
sage: len(f)
1
sage: g = propcalc.formula("a|b")
sage: len(g)
3

Component: symbolics

Keywords: logic, symbolics, propositional formula

Author: Medha Sharma, Dave Morris

Branch: 8e331fa

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/28053

[videlec]

comment:2

As #28052 comment:3.

[embray]

comment:3

Ticket retargeted after milestone closed

[DaveWitteMorris]

Branch: public/28053

[DaveWitteMorris]

Commit: 8e331fa

[DaveWitteMorris]

Changed author from Medha Sharma to Medha Sharma, Dave Morris

[DaveWitteMorris]

comment:5

This patch defines the __len__() attribute of a Boolean formula to be the length of the formula. So len(f) is the length of the formula f. This is the number of operators plus the number of variables (counting multiplicity). Parentheses and spaces in the formula are ignored.

sage: f = propcalc.formula("a")
sage: len(f)
1
sage: g = propcalc.formula("a|b")
sage: len(g)
3

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New commits:

8e331fa

define __len__() atrribute