(a) let a be a smallest element of S, i.e. there is no x in S such that x ← a, then P(a) is true,
(b) for each element s in S, if P(x) is true for each x in S with x ← s, and from this it follows that P(s) is true,
then P(s) is true for all s in S. Structural induction tends to be used in proving properties of recursive programs.
"structural induction." A Dictionary of Computing. . Encyclopedia.com. (August 15, 2018). http://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/structural-induction
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