>
>
> In particular, Jeroen, concerning the strange rule that _lmul_ not being
> implemented means that it returns None: I seem to recall (but I am not
> 100% sure) that P._get_action_(Q) (or some other method name, I don't
> recall) could test what happens if P.zero()._lmul_(Q.zero()) or similar
> things are doing, and depending on the result would conclude that an
> action does not exist or does exist, for general elements of P and Q.
>
You seem to refer to this part of the code of `detect_element_action(...)`:
cdef Element x
if X_el is None or (parent(X_el) is not X):
x = an_element(X)
else:
x = X_el
if x is None:
raise RuntimeError("an_element() for %s returned None" % X)
if Y_el is None or (parent(Y_el) is not Y):
y = an_element(Y)
else:
y = Y_el
if y is None:
if isinstance(Y, Parent):
raise RuntimeError("an_element() for %s returned None" % Y)
else:
return # don't know how to make elements of this type...
if isinstance(x, ModuleElement) and isinstance(y, Element):
# Elements defining _lmul_ and _rmul_
try:
return (RightModuleAction if X_on_left else LeftModuleAction)(Y,
X, y, x)
except CoercionException as msg:
_record_exception()
>
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