       Solve output depends on previous attempt with bad syntax

• To: mathgroup at smc.vnet.net
• Subject: [mg132501] Solve output depends on previous attempt with bad syntax
• From: Alain Cochard <Alain.Cochard at unistra.fr>
• Date: Thu, 3 Apr 2014 02:16:01 -0400 (EDT)
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```First, the correct solution of a linear system of 2 equations with 2
unknowns, for reference.

Mathematica 9.0 for Linux x86 (64-bit)

In:= Solve[{y1==a x1 +b, y2==a x2 +b},{a,b}]

-y1 + y2          x2 y1 - x1 y2
Out= {{a -> -(--------), b -> -(-------------)}}
x1 - x2              x1 - x2

Now, starting a new Mathematica session, assume I make a mistake, using '='
instead of '==', I get an error message -- so far, so good:

Mathematica 9.0 for Linux x86 (64-bit)

In:= Solve[{y1=a x1 +b, y2=a x2 +b},{a,b}]

Solve::naqs: b + a x1 && b + a x2 is not a quantified system
of equations and inequalities.

Out= Solve[{b + a x1, b + a x2}, {a, b}]

Realizing my mistake, I retry with the proper syntax:

In:= Solve[{y1==a x1 +b, y2==a x2 +b},{a,b}]

Out= {{}}

which is obviously not the correct result.

Is there a rationale here, i.e., could I have anticipated this output?

Thank you,
Alain

--
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```

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