12/26/13
The program, widgets, or Notes, should be accompanied by a suitable textbook, such as:
M.Bergmann, J.Moor, J.Nelson, The Logic Book
A.Hausman, H.Kahane, P.Tidman, Logic and Philosophy
W.Hodges, Logic
C.Howson, Logic with Trees
R.C.Jeffrey, Formal Logic: Its Scope and Limits
H.Leblanc and W.Wisdom, Deductive Logic
B.Mates, Elementary Logic
M.D.Resnick, Elementary Logic
Unfortunately these textbooks use slightly different choices of rules and symbols one from another. To adjust to this the Notes are in different major sections, with the sections tailored to particular texts.
You are invited to review
Notation
Not all logicians, and logical texts, use the same symbols for the so-called 'logical connectives'. Nor do they use the same sequences of symbols for 'well formed formulas'.
Here are typical possibilities for symbols
'not' : ∼ (the 'tilde'), ¬ (looks like the top right corner of a box)
'and': ∧, & (the ampersand), . (just a period)
'or': ∨ (usually just this, vel)
'implication': ⊃ , →
'equivalence': ≡, ↔
'existential quantifier': ∃, ∑
'universal quantifier':∀, ∏
So, in a logic book, you might see (A&B)→C and that is just the same as (A∧B)⊃C.
And you might see (∀x)(Fx ⊃ Gxy) and that might be just the same as ∀x(F(x)→G(x,y)).
The software running here can easily manage or render any of these. But we should explain what we favor, and help you find what you prefer.
The 'howson' system
The Colin Howson book uses a notation like R(a,b,c) for the application of a predicate R to the arguments or terms a, b, c. It employs the upper case letters A-Z, perhaps followed by subscripts, to be predicates, so, for example, R, S₁, T₁2 are all predicates. Variables consist of lower case [w-z] only, optionally followed by subscripts. There are no parentheses around the quantifiers. The howson system also uses ~, &, v, →, ≡, so a typical formula is ∀x(F(x)&~H(x) → G(x,y)).