font-style: normal">and </SPAN></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><I><B>fxj</B></I></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="font-style: normal"><B>, </B></SPAN></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="font-style: normal">this class must implement the </SPAN></SPAN></SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="font-style: normal"><B>AP_multistep_methods</B></SPAN></