<SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><I><B>method</B></I></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><I>: </I></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="font-style: normal">a class that defines two procedures </SPAN></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><I><B>deriv</B></I></SPAN></SPAN><SPAN STYLE="text-decoration: none"> </SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="