sort( a, b )
int a, b;

{int i, j, rlow, rupp, wlow, wupp, InBuff;
typekey MaxLower, MinUpper;
struct rec LastRead;
extern struct rec Buff[];

while ( b>a ) {
	rupp = wupp = b;
	rlow = wlow = a;
	InBuff = 0;
	MaxLower = MinimumKey;
	MinUpper = MaximumKey;
	i = a-1;
	j = b+1;
	/*** Partition the file ***/
	while ( rupp >= rlow ) {
		if ( rlow-wlow < wupp-rupp )
			LastRead = ReadDirect( rlow++ );
		else	LastRead = ReadDirect( rupp-- );
		if ( InBuff < M ) {
			Buff[ InBuff++ ] = LastRead;
			intsort( Buff, 0, InBuff-1 );
			}
		else {
			if ( LastRead.k > Buff[M-1].k ) {
				if ( LastRead.k > MinUpper ) j = wupp;
						else	MinUpper = LastRead.k;
				WriteDirect( wupp--, LastRead);
				}
			else if ( LastRead.k < Buff[0].k ) {
				if ( LastRead.k < MaxLower ) i = wlow;
						else	MaxLower = LastRead.k;
				WriteDirect( wlow++, LastRead);
				}
			else if ( wlow-a < b-wupp ) {
				WriteDirect( wlow++, Buff[0] );
				MaxLower = Buff[0].k;
				Buff[0] = LastRead;
				intsort( Buff, 0, M-1 );
				}
			else {	WriteDirect( wupp--, Buff[M-1] ) ;
				MinUpper = Buff[M-1].k;
				Buff[M-1] = LastRead;
				intsort( Buff, 0, M-1 );
				}
			}
		}
	while ( InBuff>0 )	WriteDirect( wupp--, Buff[--InBuff] );

	/*** sort the shortest subfile first ***/
	if (i-a < b-j)	{ sort(a,i);	a = j; }
		else	{ sort(j,b);	b = i; }
	}
return( 1 );
};