ሁለት ሕብረቁምፊዎች isomorphic ተብለው ይጠራሉ እና በአንደኛው ሕብረቁምፊ ውስጥ ያሉት ገጸ-ባህሪያቶች በአንጻራዊነት ተመሳሳይ ቅደም ተከተላቸውን ጠብቀው በሚኖሩባቸው በሁሉም ቦታዎች በማንኛውም ባህሪ (እራሱንም ጨምሮ) መተካት ከቻሉ ብቻ ።
Two strings are called isomorphic if and only if the characters in the first string can be replaced by any character (including itself) at all points of its occurrence while keeping the relative order of the characters the same.