internal Mathstage(Mathline m, int startRowId, int endRowId)
 {
     firstRow = startRowId;
     rowCount = (endRowId - startRowId);
     formuler = m;
 }
 internal Mathstage(Mathline m)
 {
     formuler = m;
     firstRow = 0;
     rowCount = (m.rowCount - firstRow) - 1;
 }