This paper studies conditions under which the operation of parallel insertion can be reversed by parallel deletion, i.e., when does the equality (L1 L2) L2 = L1 hold for languages L1 and L2. We obtain a complete characterization of the solutions in the special case when both languages involved are singleton words. We also define comma codes, a family of codes with the property that, if L2 is a comma code, then the above equation holds for any language L1 . Lastly, we generalize the notion of comma codes to that of comma intercodes of index m. Besides several properties, we prove that the families of comma intercodes of index m form an infinite proper inclusion hierarchy, the first element which is a subset of the family of infix codes, and the last element of which is a subset of the family of bifix codes.