Stringification of concatenate expressions

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if I add the following code to your suggestion LL=[[' '.join([str(a) for a in b])] for b in LL] SR(LL[0][0]) Sagemath says that the implied expression is badly formed

SR means "symbolic ring", and SR(blah) tries to convert the argument to an element of this ring. x_0 >= 0 will not be an element of any ring. Does eval(LL[0][0]) do what you want?

Emmanuel I do not understand the syntax map(lambda u,v:u(*v), vsign, zip(X,Zer)). To be clear what troubles me is not map nor the use of a lambda function. a zip() associate element by element the two objects ziped but why u(v) insert the sign inside the two element zipped -- I understand what does *v --. Why I do not understand is why u(v) dispatch the two element zipped arround the vsign.

@Cyrille, here, u is the operator (function), and v is the tuple (expression, value). Therefore u(*v) means "apply the operator(function) u to the arguments denoted by v.

For example, in the first line, the operator u is the ge function, that Sage usually prints <=, and v is the tuple (x_0, 0) ; u(*v) is therefore ge(x, 0), which Sage prints x_0 <= 0.

There is no bloody sign,just a function (operator) and its arguments (operands). The only unusual things are :

• the fact that <= syntax denotes an arithmetic operator, and

• the fact that <= is not acceptable as a Python identifier.

Is that clearer ?

If not, try to read a short tutorial on functional languages ; Lisp (1957) being the forefather of them all, a good Lisp tutorial might be my prescription...