Does the kleene-star's potence 0 fulfill a disjunction?

Question

Does the regular expression X•(Y*+Z) accept the word X?

I would say it does, as Y=ε should fulfill the disjunction, but I'm not sure.

score 2 · Accepted Answer · answered Mar 20 '18 at 21:35

2

Yes, matching 0 times still counts as success.

Or, looking at it from the other direction, your regex generates

X
XY
XZ
XYY
XYYY
XYYYY
...

answered Mar 20 '18 at 21:35

melpomene

84,125
8
85
148

score 1 · Answer 2 · answered Mar 20 '18 at 20:50

This answer is assuming that your regex could also be represented as X.(Y*|Z) in addition to your original of X•(Y*|Z) -- if that is not correct, please explain what • is supposed to do or represent.

X•(Y*|Z) necessitates that X be present before Y* or Z can match, but will not include X in the match's specific capture-group results, only the matching line. If you wanted to include X, you might re-write it as (X)•(Y*|Z) and extract X from capture group 1, and your disjunction match in capture group 2.

Thanks for your answer. The • is meant to be the conjunction (logical AND). I will change my `|` to make that more intuitive. — Corbie, Mar 21 '18 at 04:22

Does the kleene-star's potence 0 fulfill a disjunction?

2 Answers2