Code shared from the Lua Playground(https://lua-playground.abby.md)

playground.lua

local function equivalent(stack)
    local a, b = stack.a, stack.b

    if type(a) ~= 'table' then return a == b end
    if a == b then return true end

    local top = stack.next
    while top ~= nil do
        if stack.a == a and stack.b == b then return true end
        top = stack.next
    end

    local counta, countb = 0, 0

    for k,va in pairs(a) do
        if not equivalent({a = va, b = b[k], next = stack}) then return false end
        counta = counta + 1
    end

    for _,_ in pairs(b) do countb = countb + 1 end

    return counta == countb
end

t = setmetatable({}, {
    __newindex = function(tbl, key, value)
        for k, _ in pairs(tbl) do
            if equivalent({a = k, b = key}) then rawset(tbl, k, value); return end
        end
        rawset(tbl, key, value)
    end,
    __index = function(tbl, key)
        for k, v in pairs(tbl) do
            if equivalent({a = k, b = key}) then return v end
        end
    end
})

s = {}
s[s] = s
r = {}
r[r] = r
q = {}
q[s] = q
print(equivalent({a = s, b = s}), equivalent({a = r, b = q}), '<br />')

t[{a = 1}] = 4
t[{a = 1}] = 5
t[{a = 2}] = 6
t[q] = 7
t[s] = 6
print(t[{a = 1}], '<br />')
print(t[{a = 1, b = 2}], '<br />')
print(t[r], '<br />')
for k, v in pairs(t) do
    print(k, v, '<br />')
end