My candidate would be the (internal) direct sum of subspaces $U \oplus V$ in linear algebra. As an operator it is equivalent to sum but with the side effect of implying that $U \cap V = \lbrace 0\rbrace$. Whenever I had a chance to teach linear algebra I found this terribly confusing for students.
My candidate would be the direct sum $U \oplus V$ in linear algebra. As an operator it is equivalent to sum but with the side effect of implying that $U \cap V = \emptyset$. lbrace 0\rbrace$. Whenever I had a chance to teach linear algebra I found this terribly confusing for students. 1 [made Community Wiki] My candidate would be the direct sum$U \oplus V$in linear algebra. As an operator it is equivalent to sum but with the side effect of implying that$U \cap V = \emptyset\$. Whenever I had a chance to teach linear algebra I found this terribly confusing for students.