Logical Symbols
A ? B means if A is true then B is also true; if A is false then nothing is said about B.
→ may mean the same as ? (the symbol may also indicate the domain and codomain of a function; see table of mathematical symbols).
? may mean the same as ? (the symbol may also mean superset).
A ? B means A is true if B is true and A is false if B is false.
The statement ?A is true if and only if A is false.
The statement A ∧ B is true if A and B are both true; else it is false.
The statement A ∨ B is true if A or B (or both) are true; if both are false, the statement is false.
? x: P(x) means P(x) is true for all x.
? x: P(x) means there is at least one x such that P(x) is true.
?! x: P(x) means there is exactly one x such that P(x) is true.
x ? y means y is derived from x.