From the definition of one-to-one functions we can write that a given function f(x) is one-to-one if A is not equal to B then f(A) is not equal f(B) where A and B are any values of the variable x in the domain of function f. read more
function. To distinguish the graphs of functions from other curves, we say that a function is well defined provided one has clearly specified exactly one element in the co-domain for each element of the domain (x 2 + y = 1 does not define a function since a vertical line crosses its graph in two places). Often we denote the function or rule by f. read more