SPAN></SPAN><SPAN STYLE="text-decoration: none"> </SPAN><SPAN STYLE="text-decoration: none"><SPAN LANG="en-US"><SPAN STYLE="font-style: normal">interface (trait);</SPAN></SPAN></SPAN></FONT>
   <FONT SIZE=4 STYLE="font-size: 16pt"><SPAN LANG="en-US"><I><B>def deriv(df: Array[Double], n: Int, x: Array[Double], </B></I></SPAN></FONT>
                    <FONT SIZE=4 STYLE="font-size: 16pt"><SPAN LANG="en-US"><I><B>y: Array[Double]): Unit</B></I></SPAN></FONT>
                   <FONT SIZE=4 STYLE="font-size: 