<number>::=<digit>[<rnumber>]
    |<decimalsep><rdecimal>;
<rnumber>::=<digit>[<rnumber>]
    |<decimalsep><rdecimal>;
<rdecimal>::=<digit>[<rdecimal>];
<digit>::={0-9};
<decimalsep>::={,\.};
<variable>::='col','row';
<cell>::='['<expr>'';''<expr>']';
<function>::='sum','avg','max','min','prod','var','sd','svar','ssd' '('<cell>','<cell>')'
    |'sqrt','ln','exp','sin','cos','tan','abs','ceil','floor','log' '('<expr>')';
<<expr>>::=<expr2>['+','-'<expr>];
<expr2>::=<expr1>['*','/'<expr2>];
<expr1>::=<expr0>['^'<expr1>];
<expr0>::=['-']<element>;
<element>::=<pexpr>
    |<number>
    |<variable>
    |<cell>
    |<function>;
<pexpr>::='('<expr>')';
