Biresidual p ↔ q can be used to characterize the
similarity between p and q. Now, we are going to
recall further properties in terms of the biresidual re-
lated to the left-continuous triangular norm.
Lemma 2.
29,30,31
Assume that T is a left-continuous
triangular norm and ρ is the biresidual associated
with T . Then, for any x, y, z, o ∈ [0, 1]:
(1) x ↔ 1 = x;
(2) x = y ⇔ x ↔ y = 1;
(3) x ↔ y = y ↔ x;
(4) x ↔ y 6 R(x, 0) ↔ R(y, 0)
(5) T (x ↔ y, y ↔ z) 6 x ↔ z;
(6) (x ↔ y) ∧ (z ↔ o) 6 (x ∨z) ↔ (y ∨ o);
(7) T (x ↔ y, z ↔ o) 6 T (x, z) ↔ T(y, o);
(8) T (x ↔ y, z ↔ o) 6 R(x, z) ↔ R(y, o).
Lemma 3.
28
Assume that two arbitrary functions
are h
1
, h
2
: O → [0, 1], ρ is the biresidual and a non-
empty set is O. Then
(1)
∧
o∈O
h
1
(o) ↔ h
2
(o)
6
∧
o∈O
h
1
(o) ↔
∧
o∈O
h
2
(o);
(2)
∧
o∈O
h
1
(o) ↔ h
2
(o)
6
∨
o∈O
h
1
(o) ↔
∨
o∈O
h
2
(o).
Molodtsov presented the theory of soft set for hand-
ing uncertainties
11
. Assume that U is an initial uni-
verse set and E is parameters on the universal set.
(U, E) is called a soft space.
Definition 3.
11
The pair ( f , S) is said to be a soft set
over U if S ⊆ E and f : S → P(U).
That is to say, soft set in Definition 3 is a parame-
terized family of subsets of universe set. In general,
the parameters of a soft space are fuzzy words or
sentences associated with fuzzy words. With this in
mind, Maji et al. gave the definition of fuzzy soft
set
17
.
Definition 4.
17
Assume that S is subset of E, a pair
( f , S) is a fuzzy soft set over U if f : S → F(U),
where F(U) denote the set of all fuzzy subsets over
U.
In order to investigate fuzzy soft sets based ap-
proximate reasoning, Qin extended the definition of
fuzzy implication operator to fuzzy soft implication
operator
20
.
Definition 5.
20
Assume that ( f , S) and (g, T ) are
two fuzzy soft sets over U and V respectively.
A fuzzy soft implication operator from ( f , S) to
(g, T ) is a fuzzy soft set (h, K) over U × V , where
K ⊆ S × T , h : K → F(U ×V ) is given by
H(s, t)(u, v) = F(s)(u) → G(t)(v)
for all (s,t) ∈ K, (u, v) ∈ U × V , and → is a fuzzy
implication operator.
Based on fuzzy soft implication operators, Qin
presented fuzzy soft inference method
20
. Triple I in-
ference methods for FSMP and FSMT are present-
ed. The related calculation formulas for FSMP and
FSMT are studied. FSMP and FSMT can be ex-
pressed as follows
20
:
FSMP: Major premise: ( f , S) → (g, T ) and Minor
premise: ( f
∗
, S). Conclusion:(g
∗
, T );
FSMT: Major premise: ( f , S) → (g, T ) and Minor
premise: (g
∗
, T ). Conclusion: ( f
∗
, S).
Where ( f , S), ( f
∗
, S) and (g, T ), (g
∗
, T ) are fuzzy
soft sets over U and V respectively. Based on the F-
SMP and FSMT, Qin presented Principle of triple I
in the following:
Principle of triple I for FSMP
20
: The conclusion
(g
∗
, T ) of FSMP is the smallest fuzzy soft set over
V satisfying
R
R
f (s)(u), g(t)(v)
, R
f
∗
(s)(u), g
∗
(t)(v)
= 1;
Principle of triple I for FSMT
20
: The conclusion
( f
∗
, S) of FSMT is the largest fuzzy soft set over U
satisfying
R
R
f (s)(u), g(t)(v)
, R
f
∗
(s)(u), g
∗
(t)(v)
= 1;
Theorem 4.
20
Assume that the implication operator
in FSMP and FSMT is the residual implication R of
left-continuous t-norm T .
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International Journal of Computational Intelligence Systems, Vol. 11 (2018) 1111-1122