       Re: Matching Or expressions

• To: mathgroup at smc.vnet.net
• Subject: [mg72271] Re: [mg72250] Matching Or expressions
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 17 Dec 2006 06:20:33 -0500 (EST)
• Reply-to: hanlonr at cox.net

```numberOfSolutions[x_] := Module[
{y = LogicalExpand[x]},
If[Head[y] === Or, Length[y], 1]];

Bob Hanlon

---- "Johan GrÃ¶nqvist" <johan.gronqvist at gmail.com> wrote:
> The context of my problem is explained below.
>
> I wish to distinguish expressions of the form And[p,q] from those of the
> form Or[p,q], but the only thing I find is
> MatchQ[myExpr, Or[_]]
> and to my surprise I see that MatchQ[And[p,q],Or[_]] is True. Thus I can
> not use this to match only the Or-expressions.
>
> Thanks
>
> Johan
>
> The context is as follows:
>
> I wish to find the number of solutions to a  diophantine equation with a
> finite number of solutions.
>
> I do the following
> sols = Reduce[eqns, vars, Integers]
> and this gives me an expression that normally looks like Or[_,_,_] if
> there are several solutions, or something else if there are not.
>
> Now I wish to find the number of solutions using
> Which[MatchQ[sols, Or[_]], Length[sols], DoOtherStuff]
>
> The problem is that the MatchQ[ expr, Or[_] ] also matches e.g. (x==2 &&
> y==4), which is only one solution.
>

```

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