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A function H that maps an arbitrary length message M to a fixed length message digest MD is a collision-free hash function if 1. It is a one-way hash function. 2. It is hard ...

A semigroup with a noncommutative product in which no product can ever be expressed more simply in terms of other elements.

An occurrence of a variable in a logic formula which is not inside the scope of a quantifier.

WireWorld is a two-dimensional four-color cellular automaton introduced by Brian Silverman in 1987. The rule for the automaton uses the cell's old value a together with the ...

A set having the largest number k of distinct residue classes modulo m so that no subset has zero sum.

A braid in which strands are intertwined in the center and are free in "handles" on either side of the diagram.

An occurrence of a variable in a logic which is not free. Bound variables are also called dummy variables.

A module having dual properties with respect to a free module, as enumerated below. 1. Every free module is projective; every cofree module is injective. 2. For every module ...

A group acts freely if there are no group fixed points. A point which is fixed by every group element would not be free to move.

A positive integer n is kth powerfree if there is no number d such that d^k|n (d^k divides n), i.e., there are no kth powers or higher in the prime factorization of n. A ...