Sets, functions, continuity, sequences, series

Economics borrows its basic language from set theory and analysis. A set is a collection of distinct objects; a function assigns each element of its domain exactly one value; continuity means small changes in input give small changes in output, with no jumps. Sequences list values in order, and series add them up. Worked example: the sequence 1, 1/2, 1/4, 1/8, ... is geometric with ratio 1/2, and its infinite sum is 1/(1 - 1/2) = 2.