deq
.EQ thing1 thing2
outputs TRUE if its two inputs are the same datum, so that applying a
mutator to one will change the other as well. Outputs FALSE otherwise,
even if the inputs are equal in value.
WARNING: Primitives whose names start with a period are DANGEROUS.
Their use by non-experts is not recommended. The use of mutators
can lead to circular data structures, infinite loops, or Logo crashes.