<<graphic>>::='graphic' '{' <expr> ';' <valuedef> '}';
<valuedef>::=<varrange>[<valuedef>]|<constvalue>[<valuedef>];
<varrange>::= <var> 'from' <number> 'to' <number> 'by' <number> ';';
<constvalue>::=<const>'='<number> ';';
<number>::=<sdigit>[<rnumber>];
<rnumber>::=<digit>[<rnumber>]|<decimalsep><rdecimal>;
<rdecimal>::=<digit>[<rdecimal>];
<sdigit>::={-0-9};
<digit>::={0-9};
<decimalsep>::={,\.};
<var>::={xyz};
<const>::=<letter>[<rconst>];
<rconst>::=<allchar>[<rconst>];
<letter>::={a-w};
<allchar>::={0-9a-z};
<expr>::=<expr2>['+','-'<expr>];
<expr2>::=<expr1>['*','/'<expr2>];
<expr1>::=<expr0>['^'<expr1>];
<expr0>::=['-']<element>;
<element>::=<pexpr>|<number>|<const>|<var>;
<pexpr>::='('<expr>')';
