ot trapped (default), mixing floats and Decimals is
permitted in the Decimal() constructor, context.create_decimal() and
all comparison operators. Both conversion and comparisons are exact.
Any occurrence of a mixed operation is silently recorded by setting
FloatOperation in the context flags.  Explicit conversions with
Decimal.from_float() or context.create_decimal_from_float() do not
set the flag.

Otherwise (the signal is trapped), only equality comparisons and explicit
conversions are silent. All other mixed operations raise FloatOperation.
r)