Definition:Chain


 * Order Theory:
 * A chain is a totally ordered subset $\struct {T, \preceq}$ of an ordered set $\struct {S, \preceq}$.


 * Physics:
 * A chain is an idealized inelastic thread whose stiffness and width (but not mass) are approximated to zero.
 * Chain (Linear Measure): imperial unit of length: $1$ chain $= 22$ yards.


 * Number Theory:
 * A sociable chain is a sequence of positive integers such that the $n + 1$th term is the aliquot sum of the $n$th.