#pragma comment(linker, "/STACK:1024000000,1024000000")#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<map>#include<set>#include<queue>#include<stack>#include<iostream>using namespace std;typedef long long LL;const double pi=acos(-1.0),eps=1e-6;void File(){    freopen("D:\\in.txt","r",stdin);    freopen("D:\\out.txt","w",stdout);}template <class T>inline void read(T &x){    char c=getchar(); x=0;    while(!isdigit(c)) c=getchar();    while(isdigit(c)) {x=x*10+c-‘0‘; c=getchar();}}LL mod=1e9+7;const int maxn=1200010;int n,k;LL f[maxn],a[maxn];struct X { int L,R; }s[maxn];int c[maxn],b[maxn],sz;LL ans[maxn];int lowbit(int x){return x&(-x);}int sum(int x){    int res=0;    while(x>0) res=res+c[x],x=x-lowbit(x);    return res;}void update(int x,int v){    while(x<=1200000) c[x]=c[x]+v,x=x+lowbit(x);}LL extend_gcd(LL a,LL b,LL &x,LL &y){    if(a==0&&b==0) return -1;    if(b==0){x=1;y=0;return a;}    LL d=extend_gcd(b,a%b,y,x);    y-=a/b*x;    return d;}LL mod_reverse(LL a,LL n){    LL x,y;    LL d=extend_gcd(a,n,x,y);    if(d==1) return (x%n+n)%n;    else return -1;}int get(int x){    int L=0,R=sz-1,pos=0;    while(L<=R)    {        int mid=(L+R)/2;        if(b[mid]<x) L=mid+1;        else if(b[mid]==x) pos=mid,R=mid-1;        else R=mid-1;    }    return pos+1;}bool cmp(X a,X b) { return a.L<b.L; }int main(){    scanf("%d%d",&n,&k);    f[0]=1; for(int i=1;i<=400000;i++) f[i]=i*f[i-1]%mod;    for(int i=k;i<=400000;i++)    {        LL fz=f[i]%mod,fm=f[k]*f[i-k]%mod;        LL ni=mod_reverse(fm,mod);        a[i]=fz*ni%mod;    }    for(int i=1;i<=n;i++)    {        scanf("%d%d",&s[i].L,&s[i].R);        b[sz++]=s[i].L, b[sz++]=s[i].R;        b[sz++]=s[i].L-1; b[sz++]=s[i].L+1;        b[sz++]=s[i].R-1; b[sz++]=s[i].R+1;    }    sort(b,b+sz);    sort(s+1,s+1+n,cmp);    int h=1;    for(int i=1;i<=sz;i++)    {        while(h<=n&&get(s[h].L)==i)        {            update(get(s[h].R),1);            h++;        }        ans[i]=a[sum(1200000)-sum(i-1)];    }    LL Ans=0;    for(int i=0;i<sz;)    {        int pos=-1;        for(int j=i;j<sz;j++)        {            if(b[j]>b[i]) { pos=j; break; }        }        if(pos==-1) { Ans=(Ans+ans[i+1])%mod; break; }        Ans=(Ans+(b[pos]-b[i])*ans[i+1]%mod)%mod;        i=pos;    }    printf("%lld\n",Ans);    return 0;}