buglist 7142 exp^log(x) Cannot take first of an empty list update

WS> ElementaryFunctionCategory(): Category == with
WS>     log : $ -> $       ++ log(x) returns the natural logarithm of x.
WS>     exp : $ -> $       ++ exp(x) returns %e to the power x.
WS>     "**": ($, $) -> $  ++ x**y returns x to the power y.
WS>  add
WS>    if $ has Monoid then
WS>      x ** y == exp(y * log x)