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int unify2(struct term *t1, struct context *c1, struct term *t2, struct context *c2, struct trail **trp);
struct rel * unify_lambda(struct term *t1, struct context *c1,
                struct term *t2, struct context *c2, struct trail **trp, struct trail *tpos);
int term_ident2(struct term *t1,struct term *t2, int depthflag);  // used in match              
void forbid(struct term *x, struct context *c1, struct term *y, struct context *c2);
int forbidden2(int vn, struct context *c1, int vn2, struct context *c2);
struct term *newvar(struct context *c1, struct context *c2);
struct term *newvar2(struct context *c1, struct context *c2);
void split_or(struct clause *);
void split_and(struct clause *);
void split_not_or(struct clause *);
void split_not_and(struct clause *);
int max_vars(struct clause *c, struct term *t);
void undo_forbidden(struct trail *tp);
void fix_forbidden(int i, struct context *c1, int j, struct context *c2, struct trail *tr);
void restore_vars(struct context *c1, struct context *c2, int saveit1, int saveit2);
void free_int_list(struct int_ptr *p);
void free_forbidden(struct context *c);
void validate_context(struct context *c);  // for debugging only
#define V(c1,c2) {validate_context(c1); validate_context(c2);} 
int distinct_free_vars(struct clause *c); 
int match2(struct term *t1,struct context *c1,struct term *t2,struct trail **trp); 
int occur_check2(int varnum, struct context *c1, struct term *t, struct context *c2);
int binding_depth(struct clause *c);
void rename3(struct term *t, struct context *c);


/* restrictdata is defined as int_ptr,  so each entry forbidden[varnum] 
in a context is a linked list of integers.  Each entry in that list represents 
a variable or a constant forbidden to varnum in that context.  The entry in 
that list is manipulated using the following macros.  (We use a list of 
integers instead of a list of more structured objects to avoid modifying
McCune's Otter files any more than necessary.)
*/

// in these macros, "F" for "Forbidden"  
#define  FISVAR(x)   (((x) & (1UL << 31)) ? 1 : 0)
#define  FSETVAR(x)  (int)(( (x) |= (1UL << 31)))
#define  FSETCONSTANT(x)  ( (x) &= 0x7ffffffU)
#define  FSYMNUM(x) ((x) & 0x7ffffff)     // for storing sym_num of a constant 
#define  FSETSYMNUM(x,y)  ( x =  ((y) & 0x7ffffff))
#define  FVARNUM(x) ((x) & 0x3f)          // six nonzero bits, since varnums are < 64
#define  FSETVARNUM(x,y)  (  x = (int) ((unsigned)x & (1UL << 31)) | (((unsigned)x) & 0xffffffc0) | (y))
#define  FMULTIPLIER(x)  ((int)(((unsigned)((x) & 0x7fffffc0)) >> 6))  // 25 bits,  omitting the most significant and the 6 least significant.
         // used for storing the context multiplier of a variable  
#define  FSETMULTIPLIER(x,y) (x = (((y) << 6) | (((unsigned) x) & (1UL << 31)) | (((unsigned) x) & 0x3f)))

/* context multipliers stored in the forbidden list must not be longer than 25 bits then */