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Mathematics
Problem
Which one of the following conditions characterises a reflexive relation
R
R
R
on a non-empty set
A
A
A
? a)
(
a
,
b
)
∈
R
⇒
(
b
,
a
)
∈
R
(a,b)\in R \Rightarrow (b,a)\in R
(
a
,
b
)
∈
R
⇒
(
b
,
a
)
∈
R
for all
a
,
b
∈
A
a,b\in A
a
,
b
∈
A
b)
(
a
,
a
)
∈
R
(a,a)\in R
(
a
,
a
)
∈
R
for some
a
∈
A
a\in A
a
∈
A
c)
(
a
,
a
)
∈
R
(a,a)\in R
(
a
,
a
)
∈
R
for every
a
∈
A
a\in A
a
∈
A
d) If
(
a
,
b
)
∈
R
(a,b)\in R
(
a
,
b
)
∈
R
and
(
b
,
c
)
∈
R
(b,c)\in R
(
b
,
c
)
∈
R
, then
(
a
,
c
)
∈
R
(a,c)\in R
(
a
,
c
)
∈
R
for all
a
,
b
,
c
∈
A
a,b,c\in A
a
,
b
,
c
∈
A
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