Parse *pParse = pWC->pWInfo->pParse;
  while( pWhere->op==TK_AND ){
    if( !whereUsablePartialIndex(iTab,pWC,pWhere->pLeft) ) return 0;
    pWhere = pWhere->pRight;
  }
  if( pParse->db->flags & SQLITE_EnableQPSG ) pParse = 0;
  for(i=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
    Expr *pExpr;
    if( pTerm->wtFlags & TERM_NOPARTIDX ) continue;
    pExpr = pTerm->pExpr;
    if( (!ExprHasProperty(pExpr, EP_FromJoin) || pExpr->iRightJoinTable==iTab)
     && sqlite3ExprImpliesExpr(pParse, pExpr, pWhere, iTab) 
    ){
      return 1;
    }
  }
  return 0;

#  define TERM_VNULL    0x00   /* Disabled if not using stat4 */
#endif
#define TERM_LIKEOPT    0x100  /* Virtual terms from the LIKE optimization */
#define TERM_LIKECOND   0x200  /* Conditionally this LIKE operator term */
#define TERM_LIKE       0x400  /* The original LIKE operator */
#define TERM_IS         0x800  /* Term.pExpr is an IS operator */
#define TERM_VARSELECT  0x1000 /* Term.pExpr contains a correlated sub-query */
#define TERM_NOPARTIDX  0x2000 /* Not for use to enable a partial index */

/*
** An instance of the WhereScan object is used as an iterator for locating
** terms in the WHERE clause that are useful to the query planner.
*/
struct WhereScan {
  WhereClause *pOrigWC;      /* Original, innermost WhereClause */

** If left/right precedence rules come into play when determining the
** collating sequence, then COLLATE operators are adjusted to ensure
** that the collating sequence does not change.  For example:
** "Y collate NOCASE op X" becomes "X op Y" because any collation sequence on
** the left hand side of a comparison overrides any collation sequence 
** attached to the right. For the same reason the EP_Collate flag
** is not commuted.
**
** The return value is extra flags that are added to the WhereTerm object
** after it is commuted.  The only extra flag ever added is TERM_NOPARTIDX
** which prevents the term from being used to enable a partial index if
** COLLATE changes have been made.
*/
static u16 exprCommute(Parse *pParse, Expr *pExpr){
  u16 expRight = (pExpr->pRight->flags & EP_Collate);
  u16 expLeft = (pExpr->pLeft->flags & EP_Collate);
  u16 wtFlags = 0;
  assert( allowedOp(pExpr->op) && pExpr->op!=TK_IN );
  if( expRight==expLeft ){
    /* Either X and Y both have COLLATE operator or neither do */
    if( expRight ){
      /* Both X and Y have COLLATE operators.  Make sure X is always
      ** used by clearing the EP_Collate flag from Y. */
      pExpr->pRight->flags &= ~EP_Collate;
      wtFlags |= TERM_NOPARTIDX;
    }else if( sqlite3ExprCollSeq(pParse, pExpr->pLeft)!=0 ){
      /* Neither X nor Y have COLLATE operators, but X has a non-default
      ** collating sequence.  So add the EP_Collate marker on X to cause
      ** it to be searched first. */
      pExpr->pLeft->flags |= EP_Collate;
      wtFlags |= TERM_NOPARTIDX;
    }
  }
  SWAP(Expr*,pExpr->pRight,pExpr->pLeft);
  if( pExpr->op>=TK_GT ){
    assert( TK_LT==TK_GT+2 );
    assert( TK_GE==TK_LE+2 );
    assert( TK_GT>TK_EQ );
    assert( TK_GT<TK_LE );
    assert( pExpr->op>=TK_GT && pExpr->op<=TK_GE );
    pExpr->op = ((pExpr->op-TK_GT)^2)+TK_GT;
  }
  return wtFlags;
}

/*
** Translate from TK_xx operator to WO_xx bitmask.
*/
static u16 operatorMask(int op){
  u16 c;

          pTerm->eOperator |= WO_EQUIV;
          eExtraOp = WO_EQUIV;
        }
      }else{
        pDup = pExpr;
        pNew = pTerm;
      }
      pNew->wtFlags |= exprCommute(pParse, pDup);
      pNew->leftCursor = aiCurCol[0];
      pNew->u.leftColumn = aiCurCol[1];
      testcase( (prereqLeft | extraRight) != prereqLeft );
      pNew->prereqRight = prereqLeft | extraRight;
      pNew->prereqAll = prereqAll;
      pNew->eOperator = (operatorMask(pDup->op) + eExtraOp) & opMask;
    }

} {1}
do_execsql_test index6-15.4 {
  SELECT 1 FROM t0 WHERE FALSE BETWEEN FALSE AND (t0.c0 IS FALSE);
} {1}
do_execsql_test index6-15.5 {
  SELECT 1 FROM t0 WHERE (c0 IS FALSE) IN (FALSE);
} {1}

# 2019-09-03
# Ticket https://sqlite.org/src/info/767a8cbc6d20bd68
do_execsql_test index6-16.1 {
  DROP TABLE t0;
  CREATE TABLE t0(c0 COLLATE NOCASE, c1);
  CREATE INDEX i0 ON t0(0) WHERE c0 >= c1;
  INSERT INTO t0 VALUES('a', 'B');
  SELECT c1 <= c0, c0 >= c1 FROM t0;
} {1 0}
do_execsql_test index6-16.2 {
  SELECT 2 FROM t0 WHERE c0 >= c1;
} {}
do_execsql_test index6-16.3 {
  SELECT 3 FROM t0 WHERE c1 <= c0;
} {3}




finish_test