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The book review continues
LANGER, SUSANNE K (1953)(1967) An Introduction to Symbolic Logic, Dover Publications, New York. (Philosophy)
Key symbols
≡df = Equivalence by definition
: = Equal (s)
ε = Epsilon and means is
⊃ = Is the same as
⊨ is Entails
˜ = Not
∃ = There exists
∃! = There exists
∴ = Therefore . = Therefore
< = Is included
v = a logical inclusive disjunction (disjunction is the relationship between two distinct alternatives).
x = variable = Conjunction meaning And 0
= Null class
cls = Class
int = Interpretation
Langer, page 212. Here addition and multiplication are being expressed through commutation, as equal, therefore, (a x b) + (a x c) is equated as (a x (b + c). |
Using
(a x b) + (a x c)
and then
(a x (b + c)
Consider
(3 x 3) + (3 x 3) equals 18
(3 x (3 + 3) equals 18
In earlier reviews, a, b, c were all equated.