But what do you mean with lexicals? Could you give a "simple" example? Thank you.

Short for "lexical variables". 

my $var;

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RungeKutta needs \&in_2 in its own call.

Not a problem. See the solution I added to my original post in this thread.

In reply to Re^4: Closures and undefined subs by ikegami
in thread Closures and undefined subs by Anonymous Monk

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