[texhax] amstex question

[Zbigniew Nitecki]

I am trying to align four long lines of formula, where the item in  
the first line being aligned is inside a set of delimiters.  I tried  
breaking this up, using \right. and \left . where appropriate (and  
using size commands to make sure the size of the delimiters is  
correct, but somehow amstex is looking for a closing brace:  I can't  
find where the "opening" brace that prompts it to do so is located.

Here is my tex source;  I include definitions of my commands being used
************************************************************************ 
*****************************
\newcommand{\pddat}[3]{\frac{\partial#1}{\partial#2}\left(#3\right)}
\newcommand{\delx}{\triangle x}
\newcommand{\dely}{\triangle y}
	\begin{equation*}
	\begin{split}
		\fof{x+\delx,y+\dely}-\biggl(\fof{x,y}\right.
			&+\left.\pddat{f}{x}{x,y}\delx
			+\pddat{f}{y}{x,y}\dely\right)\\
		=\biggl(\fof{x+\delx,y+\dely}-\fof{x,y}\biggr)
			&-\left(\pddat{f}{x}{x,y}\delx
			+\pddat{f}{y}{x,y}\dely\right)\\
			=\left(\pddat{f}{x}{x+\delts{1},y+\dely}\delx
			+\pddat{f}{y}{x,y+\delts{2}}\dely\right)
			&-\left(\pddat{f}{x}{x,y}\delx
			+\pddat{f}{y}{x,y}\dely\right)\\
			=\left(\pddat{f}{x}{x+\delts{1},y+\dely}-\pddat{f}{x}{x,y}\right) 
\delx
				&+\left(\pddat{f}{y}{x,y+\delts{2}}-\pddat{f}{y}{x,y}\right)\dely.
	\end{split}
	\end{equation*}

************************************************************************ 
****************************
and here is the error message:
*****************************************
! Missing } inserted.
<inserted text>
                 }
l.243 	\end{split}
******************************************
in TexShop, when I then go into nonstop mode ("r") the formula  
compiles fine, looking as I intended.  If I break the stuff into two  
separate equation*/split environments, with the first set the first  
two lines (ie, break after the second \\), then the same occurs, but  
if I then comment out the first of these two, I get no error.   
Clearly the problem is in the first "line", but I can't figure it out.

Any ideas, on a cause and/or a fix?

Zbigniew Nitecki
Department of Mathematics
Tufts University
Medford, MA 02155

telephones:
Office    (617)627-3843
Dept.    (617)627-3234
Dept. fax    (617)627-3966


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