Induction vs Recursion

Induction is bottom-up.

Recursion is top-down.

In parsing, YACC is bottom-up, PEG[1] is top-down.

YACC is LR(k), PEG is recursive-descent.

YACC is context-free, PEG can depend on context.

LR(k) is theoretical, PEG is practical.

Semi-colons exist in PL[2]s because of YACC.  PEG doesn't require semi-colons in PLs.

Possible rewording: top-down is operational, whereas bottom-up is declarative[3].

Top-down implies the use of a Stack[4].  Bottom-up does not.

[Use of a Stack defies parallelism.]

"Context free" means that time[5] has been removed, there is no f(t).[6]

[1] PEG means Parsing Expression Grammar, see  PEG is like REGEXPs on steroids.

[2] PL means Programming Language.

[3] Question to self: Is this a correct characterization?

[4] A stack of breadcrumbs - to "remember" where you were.

[5] Time is also known as History.  History is also known as State.

[6] Lack of f(t) has been decried by Ilya Prigogene (Nobel laureate, "Order Out of Chaos") and Grace Hopper.