database theory – How to find all tuples in which some attribute appears more than three times


im havin trouble with this exercise. I have a table like this and i can only use relational algebra without aggregate function like sum, count, etc.

Name | x

a ~~ 1

b ~~ 2

c ~~ 1

d ~~ 1

e ~~ 2

f ~~ 2

g ~~ 3

h ~~ 3

i ~~ 4

i need to get the values of x if it appears three times or more. In this case the output would be {1,2}

I have this

R1 = π x1←x, name1←name table

R2 = π x1, name (R1 ⨝ x1 = x ∧ name1 ≠ name table)

but this just gets the values of x that appear more than once.
Thanks.