From ApCoCoAWiki


check if one object is contained in another


The semantics of IsIn is explained in the following table:


  | POLY   IsIn  IDEAL   checks for ideal membership.              |
  | VECTOR IsIn  MODULE  checks for module membership.             |
  | OBJECT IsIn  LIST    checks if the list contains the object.   |
  | STRING IsIn  STRING  checks if the first string is a substring |
  |                      of the second one.                        |
                      IsIn operator



E IsIn F

where E and F are CoCoA objects.  For a precise description of
allowable objects, see the full online help entry.